NEW YORK — The federal agency overseeing the safe transport of hazardous materials released a stunning explanation of its May 11 decision striking down a Washington state effort to regulate trains carrying volatile oil within its borders. A state cannot use “safety as a pretext for inhibiting market growth,” wrote Paul J. Roberti, the chief counsel for the Pipeline and Hazardous Materials Safety Administration (PHMSA). The statement appeared in the Trump administration's justification for overruling Washington’s oil train regulation, which was challenged by crude-producing North Dakota and oil industry lobbying groups.